The term stent has been used interchangeably with terms such as intraluminal vascular graft and expansible prosthesis. As used throughout this specification, the term stent is intended to have a broad meaning and encompasses any expandable prosthetic device for implantation in a body passageway (e.g. a lumen or artery).
There have been various attempts at addressing the delivery and deployment of stents at bifurcated lesions. Bifurcated vessels may be of the Y-type, wherein a main branch bifurcates into two secondary branches, or of the T-type, wherein a side branch extends from a main branch. While the subject invention may be employed in certain circumstances with Y-type bifurcated vessels, it is primarily directed for use with T-type bifurcated vessels.
One common approach is to place a conventional stent in the main larger body lumen over the origin of the side branch. After removal of the stent delivery balloon, a second wire is introduced through a cell in the wall of the deployed stent and into the side branch. A balloon is then introduced into the side branch and inflated to enlarge that cell of the main vessel stent. A second stent is then introduced through the enlarged cell into the side branch and expanded therein.
Another strategy employed is the kissing balloon technique, in which separate balloons are positioned in the main and the side branch vessels and simultaneously inflated. Various two stent approaches including Culotte, T-stent and crush stent techniques have been employed as well as described in detail in U.S. Pat. No. 7,481,834 to Kaplan et al.
One of the drawbacks of the conventional stent techniques is that they run the risk of compromising the degree of the patency of the primary vessel and/or its branches or bifurcation. This may occur as a result of several problems, such as displacing disease tissue, vessel spasm, and dissection with or without intimal flaps, thrombosis, and embolism, that will increase the chance of restenosis.
These limitations have led others to develop specifically designed stents to treat bifurcation lesions. One approach employs a stent design with a side opening: U.S. Pat. Nos. 6,325,826 and 6,210,429 to Vardi et al.; U.S. Pat. No. 6,033,435 to Penn et al.; U.S. Pat. No. 6,056,775 to Borghi et al. A second approach includes a distal bifurcation of the stent: U.S. Pat. No. 4,994,071 to MacGregor; and U.S. Pat. No. 6,740,113 to Vrba. A third approach is having at least two axially aligned circumferential anchors: U.S. Pat. No. 7,481,834 to Kaplan et al.
Though these approaches have many theoretical advantages, they have shortcomings in:                (a) Accurate positioning of the stent in the main vessel and the side branched or bifurcated lesion;        (b) Adequate stent coverage which will result in high chance of restenosis;        (c) Prevention of over-stretching of the proximal main artery when double balloons are used, as in the kissing balloon technique, which can damage the artery and increase the risk of restenosis in the stent.        (d) Prevention of high metal to artery ratio resulted from crushing the struts of the main stent, in order to make an opening to access the side branch artery for deployment of the side branch stent, which increases fluid turbulence that may result in deposition of clot material which can cause blockage at the site of the bifurcation of the stent;        (e) Prevention of the plaque shifting in the bifurcated arteries during balloon inflation;        (f) In the case of the Kaplan et al. U.S. Pat. No. 7,481,834, insertion of traditional stent into a main vessel, after deployment of the new design stent in the side branched stent with anchor design, may pose a limitation to blood flow and access to the side branch vessel. The term ‘stent jail’ is often used to describe this concept.        
Another drawback is with the balloon delivery system that assists in positioning the stent with accuracy in the bifurcated lesions, particularly involved in the procedure of double balloon sequential dilation for the stent, which has not proven to be very successful. These limitations have led others to develop specifically designed balloons to treat bifurcation lesions, such as in U.S. Pat. No. 6,017,324 to Tu et al. This design has its limitations in that it will help to solve specific bifurcation lesions when the distal branches have a Y-shape and the size of the distal vessels are smaller than the size of the proximal vessel (e.g. the aortic artery at bifurcation with iliac arteries) but it is not suitable if the size of one of the distal branches is equal to the proximal vessel size, and not suitable for the side branched vessels which are the majority of the cases.
Accordingly, there is a need for an improved stent design and delivery balloon apparatus and method of deployment, most particularly for application within the cardiac, coronary, renal, peripheral vascular, gastrointestinal, pulmonary, urinary and neurovascular system, and the brain, which:                (1) Provides for a proper balloon stent delivery system and method for high accuracy for deployment of the stent in branched or bifurcated lesions;        (2) Completely covers the bifurcation point of the bifurcation vessels with a high degree of accuracy;        (3) Provides a proper balloon delivery system that will prevent overstretching of the proximal part of the main artery even where two balloons used as kissing balloons;        (4) Prevents high metal to artery ratio at the bifurcation junction, by preventing crushing the struts of the main stent, in order to create an opening in the main stent to access the side branch artery;        (5) Prevents the plaque shifting in the bifurcated arteries during balloon inflation;        (6) Allows for differential sizing of the stents in bifurcated stent apparatus even after the main stent is implanted; and        (7) Is usable to treat bifurcated vessels where the branch vessel extends from the side of the main vessel.        